Structural and material properties of human foot tendons

BackgroundsThe aim of this study was to assess the mechanical properties of the main balance tendons of the human foot in vitro reporting mechanical structural properties and mechanical material properties separately. Tendon structural properties are relevant for clinical applications, for example in orthopedic surgery to elect suitable replacements. Tendon material properties are important for engineering applications such as the development of refined constitutive models for computational simulation or in the design of synthetic materials.MethodsOne hundred uniaxial tensile tests were performed to obtain the mechanical response of the main intrinsic and extrinsic human foot tendons. The specimens were harvested from five frozen cadaver feet including: Extensor and Flexor tendons of all toes, Tibialis Anterior and Posterior tendons and Peroneus Brevis and Longus tendons.FindingsCross-sectional area, load and strain failure, Young's modulus and ultimate tensile stress are reported as a reference of foot tendon mechanical properties. Two different behaviors could be differentiated. Tibialis and Peroneus tendons exhibited higher values of strain failure compared to Flexor and Extensor tendons which had higher Young's modulus and ultimate tensile stress. Stress–strain tendon curves exhibited proportionality between regions. The initial strain, the toe region and the yield point corresponded to the 15, 30 and 70% of the strain failure respectively.InterpretationMechanical properties of the lesser-studied human foot tendons are presented under the same test protocol for different engineering and clinical applications. The tendons that work at the inversion/eversion plane are more deformable at the same stress and strain rate than those that work at the flexion/extension plane.     

Influence of gender,age, shelf-life,and conservation method on the biomechanical behavior of colon tissue under dynamic solicitation

BackgroundData from biomechanical tissue sample studies of the human digestive tract are highly variable. The aim of this study was to investigate 4 factors which could modify the mechanical response of human colonic specimens placed under dynamic solicitation until tissue rupture: gender, age, shelf-life and conservation method.MethodsWe performed uniaxial dynamic tests of human colonic specimens. Specimens were taken according to three different protocols: refrigerated cadavers without embalming, embalmed cadavers and fresh colonic tissue. A total of 143 specimens were subjected to tensile tests, at a speed of 1 m s⁻¹.FindingsYoung's modulus of the different conservation protocols are as follows: embalmed, 3.08 ± 1.99; fresh, 2.97 ± 2.59; and refrigerated 3.17 ± 2.05. The type of conservation does not modify the stiffness of the tissue (p = 0.26) but does modify the stress necessary for rupture (p < 0.001) and the strain required to obtain lesions of the outer layer and the inner layer (p < 0.001 and p < 0.05, respectively). Gender is also a factor responsible for a change in the mechanical response of the colon. The age of the subjects and the shelf-life of the bodies did not represent factors influencing the mechanical behavior of the colon (p > 0.05).InterpretationThe mechanical response of the colon tissue showed a biphasic injury process depending on gender and method of preservation. The age and shelf-life of anatomical subjects do not alter the mechanical response of the colon.     

Influence of the fixation technique on the mechanical properties of human cancellous bone of the femoral head

BackgroundThe femoral head is of central importance for the force transmission from the suprapelvic body mass to the lower extremity. However, the condition of the subcortical bone and its mechanical properties in case of pathological changes due to coxarthrosis or femoral head necrosis differ from the healthy condition.MethodsFresh femoral heads were gathered during hip total endoprosthesis surgeries and cylindrical cancellous bone samples were extracted with a hollow drill. By means of a uniaxial tensile-compression test system, the compressive strength was determined for two different specimen types (fresh and 24 h storage in acetone). Exemplary tests on an exceptionally large femoral head were performed to compare properties of fresh, fresh-deep-frozen and acetone-stored samples.FindingsThe deformation behaviour and the material parameters determined were very heterogeneous. For most of the specimens, a destructive material test was successfully carried out, i.e. the compressive strength was determined. The average strength of fresh specimens was slightly higher than that of acetone specimens. On the other hand, the average Young's modulus of the acetone specimens was higher than that of the fresh specimens.InterpretationThe lower Young's moodulus of the fresh samples compared to the acetone samples could indicate a causal effect of the degreasing influence of the acetone. The partly considerable individual differences in compressive strength and failure compression can have patient-specific influencing factors such as constitution and physical fitness as well as causes in the initial pathological condition.     

Irradiation at 11 kGy conserves the biomechanical properties of fascia lata better than irradiation at 25 kGy

The objective of this study was to determine the biomechanical properties of the fascia lata and the effects of three preservation methods: freezing, cryopreservation with dimethylsulfoxide solution and lyophilization; and to compare the effects of low-dose (11 kGy) and normal-dose (25 kGy) gamma-ray sterilization versus no irradiation.248 samples from 14 fasciae latae were collected. Freezing samples were frozen at −80 °C. Cryopreservation with dimethylsulfoxide solution samples were frozen with 10 cl dimethylsulfoxide solution at −80 °C. Lyophilization samples were frozen at −22 °C and lyophilized. Each preservation group were then randomly divided into 3 irradiation groups.The cryopreservation with dimethylsulfoxide solution samples had significantly worse results in all 3 irradiation conditions. Young's modulus was lower for the freezing samples (p < 0.001) and lyophilization samples groups (p < 0.001). Tear deformation was lower for the freezing samples (p = 0.001) and lyophilization samples groups (p = 0.003), as was stress at break (p < 0.001 and p < 0.001). Taking all preservation methods together, samples irradiated at 25 kGy had worse results than the 0 kGy and 11 kGy groups in terms of Young's modulus (p = 0.007 and p = 0.13) and of stress at break (p = 0.006 and p = 0.06).The biomechanical properties of fascia lata allografts were significantly worse under dimethylsulfoxide cryopreservation. The deleterious effects of irradiation were dose-dependent.     

Contrary response of porcine articular cartilage below and over 1000 s−1

BackgroundKnee joints experience excessive loads quite frequently during sports activities, and these shocks could accelerate progressive degeneration in articular cartilage.MethodsQuasi-static and dynamic response of porcine knee articular cartilages were investigated in this research. Split Hopkinson Pressure Bars (SHPB) were utilized to examine the articular cartilage properties at strain rates between 0.01–2000 s⁻¹.FindingsThe results showed that strain rate is an important factor for articular cartilages, distinctively divided into above and below 1000 s⁻¹. The articular cartilages exhibit a strain hardening phenomenon when shock loaded at strain rates under 1000 s⁻¹. When loaded at strain rates over 1000 s⁻¹, their ultimate strength and elastic modulus decreased with increasing strain rates.InterpretationThe biphasic structure of the cartilage explained the change of modulus. At the lower strain rates, fibers realigned and solidified the structure, while at higher strain rates, there is not enough time for the tissue fluid to move inside the cartilage, leading to a reduction in the deformability of the specimen and raising of Young's modulus. The results can be utilized to provide some useful data for biomaterial and computational works in the future.     

Mechanical properties of fused sagittal sutures in scaphocephaly

BackgroundCraniosynostosis in newborns is caused by the premature closure of the cranial sutures leading to cranial vault deformity. It results in aesthetic imbalance and developmental disabilities and surgery is frequent during the first months of growth. Our study focused on scaphocephaly defined as the premature closure of the sagittal suture. We hypothesised that the effective mechanical properties of sutures were altered as compared to those of the parietal adjacent tissue considered as control.MethodsThe population consisted of seven males and four females (mean age 4.9 months). Sixteen suture samples and thirty-four parietal tissue samples were harvested during corrective surgery and investigated by using three-point bending tests to obtain the structure-stiffness of specimens. An energy model was used to derive the effective Young's modulus. A histological study complemented the experimental protocol.FindingsFused sutures were thicker than adjacent bone and the natural curvature of sutures did not influence the static mechanical response. The stiffness of stenotic sutures was significantly higher than that of the parietal bone. The effective Young's modulus of stenotic sutures was significantly lower than that of the parietal adjacent tissue. The parietal tissue showed a parallel bone architecture whereas the central stenotic tissue was disorganised with more vascularisation.InterpretationThe stenotic suture differed in structural and mechanical terms from the adjacent bone during calvarial growth in the first year of life. Our study emphasised the alteration of effective tissue properties in craniosynostosis.     

Magnetic resonance imaging T1 and T2 mapping provide complementary information on the bone mineral density regarding cancellous bone strength in the femoral head of postmenopausal women with osteoarthritis

BackgroundSince bone mass is not the only determinant of bone strength, there has been increasing interest in incorporating the bone quality into fracture risk assessments. We aimed to examine whether the magnetic resonance imaging (MRI) T1 or T2 mapping value could provide information that is complementary to bone mineral density for more accurate prediction of cancellous bone strength.MethodsFour postmenopausal women with hip osteoarthritis underwent 3.0-T MRI to acquire the T1 and T2 values of the cancellous bone of the femoral head before total hip arthroplasty. After the surgery, the excised femoral head was portioned into multiple cubic cancellous bone specimens with side of 5 mm, and the specimens were then subjected to microcomputed tomography followed by biomechanical testing.FindingsThe T1 value positively correlated with the yield stress (σ_y) and collapsed stress (σ_c). The T2 value did not correlate with the yield stress, but it correlated with the collapsed stress and strength reduction ratio (σ_c/σ_y), which reflects the progressive re-fracture risk. Partial correlation coefficient analyses, after adjusting for the bone mineral density, showed a statistically significant correlation between T1 value and yield stress. The use of multiple coefficients of determination by least squares analysis emphasizes the superiority of combining the bone mineral density and the MRI mapping values in predicting the cancellous bone strength compared with the bone mineral density-based prediction alone.InterpretationThe MRI T1 and T2 values predict cancellous bone strength including the change in bone quality.     

Differences in the principal strain angles during activities performed on natural hilly terrain versus engineered surfaces

BackgroundTibial stress fractures in military recruits occur beginning with the fourth week of training. In and ex vivo tibial strain experiments indicate that the repetitive mechanical loading during this time may not alone be sufficient to cause stress fracture. This has led to the hypothesis that the development of tibial stress fracture is mediated by the bone remodeling response to high repetitive strains. This study assesses the differences in the strain and angle of the principal strain during military field activities versus common civilian activities.MethodsIn vivo strain measurements were made from a rosette strain gauge bonded to the midshaft of the medial tibia. Measurements of principal strains and their angles were made while performing level and inclined walking and running on an asphalt surface, while fast walking up and down stairs, while performing a standing vertical jump and while zig-zag running up and down a 30° inclined dirt hill.FindingsThe angle of the principal strain varied little (5.40° to +2.74°) during activities performed on engineered surfaces. During zig-zag running on a dirt hill the strain levels were higher (maximum shear = 4290 με). At the pivot points of zig-zag running the angle of the principal strain varied between −115° to −123° downhill and between −32.8° to −51° uphill.InterpretationActivities that mimic those performed by infantry recruits on irregular hilly surfaces result in higher tibial strains and have more variation in principal strain angles than activities of ordinary civilian life performed on engineered surfaces.     

Mechanical characterization of bone quality in distal femur fractures using pre-operative computed tomography scans

BackgroundMechanical testing of implant constructs designed to treat distal femur fractures has been hampered by a lack of clinical data on the biomechanical properties of the distal femur in patients who sustain these fractures. Therefore, the purpose of this study was to use quantitative computed tomography (qCT) to investigate the mechanical characteristics of fractured distal femurs to inform the selection of synthetic materials for biomechanical testing.MethodsDistal femur fractures treated at a Level I trauma center were retrospectively reviewed and 43 cases with preoperative CT scans were identified for analysis. Scans were segmented and each bone fragment was reconstructed as a 3D model. The Young's modulus of the distal femur was determined from voxel-based radiodensity.FindingsMedian patient age was 72 years (IQR = 57–81), with 26% males and 74% females. Young's modulus in the distal femur was negatively correlated with patient age (R² = 0.50, p < 0.001). The distribution of patient-specific modulus values was also compared with the compressive modulus ranges for graded polyurethane foams according to ASTM F1839. Bone quality ranged from Grade 25 in younger individuals to Grade 5 in older individuals.ConclusionNo single grade of synthetic polyurethane foam can be selected to model all clinically important scenarios for biomechanical testing of distal femur fracture fixation devices. Rather, this data can be used to select an appropriate material for a given clinical scenario. A Grade 25 foam is appropriate for implant longevity, whereas for implant stability, Grades 5-15 are more appropriate.     

Effects of electromechanical reshaping on mechanical behavior of exvivo bovine tendon

BackgroundElectromechanical reshaping is a novel, minimally invasive means to induce mechanical changes in connective tissues, and has the potential to be utilized in lieu of current orthopedic therapies that involve tendons and ligaments. Electromechanical reshaping delivers an electrical current to tissues while under mechanical deformation, causing in situ redox changes that produce reliably controlled and spatially limited mechanical and structural changes. In this study, we examine the feasibility of altering Young's modulus and inducing a shape deformation using an ex vivo bovine Achilles tendon model.MethodsTendon was mechanically deformed in two different modes: (1) elongation to assess for tensile modulus and (2) compression to assess for compressive modulus. Electromechanical reshaping was applied to tendon specimens via flat plate platinum electrodes (6 V, 3 min) while simultaneously under mechanical strain for 15 min.FindingsIn elongation mode, post-electromechanical reshaping samples demonstrated a significant decrease in Young's modulus compared to pretreatment samples (66.02 and 45.12 MPa, respectively, p < 0.0049). In compression mode, posttreatment samples illustrated a significant shape change, with an increase in diameter (10.62 to 11.36 mm, p < 0.05) and decrease in thickness (4.13 to 3.62 mm, p < 0.05).InterpretationResults demonstrated a tissue softening effect without lengthening deformation during elongation, and a shortening effect without compromising compressive stiffness during compression. Electromechanical reshaping's reliable, low-cost, and efficacious methodology in inducing mechanical and structural connective tissue modifications illustrates a potential for future alternative orthopedic applications. Future studies will optimize and refine electromechanical reshaping to address clinically relevant geometries and methods such as needle techniques.     

用超声声速和声衰减预测人松质骨的生物力学性质

本文介绍了用超声波声速、声衰减及两者的组合来预测人松质骨在准静态和动态加载条件下的生物力学性质的实验和分析。实验结果表明：（１）超声波的声速（ＵＶ）和声衰减（ＢＵＡ）的线性组合显然比单个ＵＶ或ＢＵＡ更能准确地预测人松质骨在准静态和动态加载条件下的力学性质；（２）松质骨试样的平均动态压缩弹性模量Ｅ、强度Ｓ分别比准静态加载时的相应力学性质参数高８２％和６３％，而松质骨试样的平均动态压缩终应变εｍ则比准静态加载时低１８％。     

Assessment of healthy trapeziometacarpal cartilage properties using indentation testing and contrast-enhanced computed tomography

BackgroundThe trapeziometacarpal joint is a common site for osteoarthritis development in the hand. When osteoarthritis is present, it results in significant functional disabilities due to the broad range of activities performed by this joint. However, our understanding of osteoarthritis initiation and progression at this joint is limited because of the current lack of knowledge regarding the properties and structure of the corresponding cartilage layers. The objective of this study is to assess the morphological and mechanical properties of trapeziometacarpal cartilage via the combination of indentation testing and contrast-enhanced computed tomography. Such research may lead to the development of medical imaging-based approaches to measure cartilage properties in vivo.MethodsIntact first metacarpals and trapezia were extracted from 16 fresh-frozen human cadaver hands. For each specimen, load-displacement behavior was measured at 9 testing sites using a standardized indentation testing device to calculate the normal force and Young's modulus of the cartilage sub-regions. The specimens were then immersed in CA4+ contrast agent solution for 48 h and subsequently scanned with a resolution of 41 μm in a HR-pQCT scanner to measure cartilage thickness and attenuation. Finally, correlations between compressive Young's modulus and contrast-enhanced computed tomography attenuation of the cartilage were assessed.FindingsNo significant difference was found in cartilage thickness between the trapezium and first metacarpal, but the comparison between articular regions showed thinner cartilage around the volar aspect of both the first metacarpal and the trapezium. The first metacarpal cartilage was stiffer than the trapezial cartilage. A significant positive correlation was observed between Young's modulus and mean contrast-enhanced CT attenuations in superficial and full-depth cartilage in both the first metacarpal and the trapezium cartilage.InterpretationThe quantitative measurements of trapeziometacarpal thickness and stiffness as well as a correlation between Young's modulus and contrast-enhanced computed tomography attenuation provides a method for the non-destructive in vivo assessment of cartilage properties, a greater understanding of thumb cartilage behavior, and a dataset for the development of more accurate computer models.     

Ex Vivo and In Vivo Assessment of the Non-linearity of Elasticity Properties of Breast Tissues for Quantitative Strain Elastography

The aim of this study was to reveal the background to the image variations in strain elastography (strain imaging [SI]) depending on the manner of manipulation (compression magnitude) during elasticity image (EI) acquisition. Thirty patients with 33 breast lesions who had undergone surgery followed by SI assessment in vivo were analyzed. An analytical approach to tissue elasticity based on the stress-elastic modulus (Young's modulus) relationship was adopted. Young's moduli were directly measured ex vivo in surgical specimens ranging from 2.60 kPa (fat) to 16.08 kPa (invasive carcinoma) under the weak-stress condition (<0.2–0.4 kPa, which corresponds to the appropriate “light touch” technique in SI investigation. The contrast (ratio) of lesion to fat in elasticity ex vivo gradually decreased as the stress applied increased (around 1.0 kPa) on the background of significant non-linearity of the breast tissue. Our results indicate that the differences in non-linearity in elasticity between the different tissues within the breast under minimal stress conditions are closely related to the variation in EI quality. The significance of the “pre-load compression” concept in tissue elasticity evaluation is recognized. Non-linearity of elasticity is an essential attribute of living subjects and could provide useful information having a considerable impact on clinical diagnosis in quantitative ultrasound elastography.     

剪切波弹性成像弹性模量间接评估干燥综合征患者腮腺功能

目的 探讨剪切波弹性成像技术间接评估干燥综合征（SS）患者腮腺功能的价值。方法 根据核素动态显像成像结果将100例SS患者分为腮腺功能正常组、轻度受损组、中度受损组及重度受损组,行剪切波弹性成像检查,获得腮腺杨氏模量值,比较4组间杨氏模量值的差异,并分析与腮腺功能的相关性,绘制ROC曲线,评价杨氏模量值诊断腮腺功能重度受损的效能。结果 4组间腮腺杨氏模量值差异有统计学意义（F=78.60,P<0.001）。腮腺杨氏模量值随腮腺功能受损程度加重而增高（r_s=0.83,P<0.001）。以38.38 kPa为临界值,杨氏模量值诊断腮腺功能重度受损的曲线下面积为0.93（P<0.001）,敏感度及特异度分别为89.3%及84.7%。结论 剪切波弹性成像技术测量的弹性模量值可间接评估SS患者腮腺功能,为临床判断及随访SS病情变化提供依据。     

股骨头负重区松质骨的压缩力学特性

背景松质骨力学特性在代谢性疾病、骨折、关节退行性变的内在发生规律中具有意义.目的了解松质骨的生物力学特性.设计以股骨标本为单一样本的实验观察.单位上海第二医科大学附属第九人民医院骨科生物力学实验室.对象2001-05/07完成于在上海第九人民医院骨科生物力学实验室,选取19具男性尸体股骨头.方法取19具新鲜青年(30岁左右)尸体股骨.对股骨头负重区的松质骨进行压缩测试.主要观察指标标本的屈服载荷、极限应力、极限应变、能量值、弹性模量.结果测算松质骨各项压缩数据,其中屈服载荷的平均值为(410.64±190.29)N,极限应力为(8.69±3.75)MPa,极限应变为(10.84±6.58)%,能量值为(2.54±1.89)J,弹性模量为(40.77±32.12)MPa.加载初期松质骨呈弹性变形,此后横截面增大抗压能力增强.结论试验表明松质骨力学性能主要是缓解外力冲击加压.     

实时剪切波弹性成像定量评价正常脾脏组织弹性

目的 探讨实时剪切波弹性成像（SWE）应用于正常脾脏组织的可行性及影响因素,并建立正常人脾脏组织的杨氏模量值参考范围。方法 对280名健康人行肝脏、脾脏弹性模量值检测,记录相关定量分析数据,收集受检者基本信息,分析其性别、年龄、体质量指数（BMI）与肝、脾弹性模量值的相关性。结果 280名健康人正常肝脏杨氏模量均值为（5.54±1.08）kPa,95% CI为（5.41,5.67）kPa;正常脾脏杨氏模量均值为（11.67±2.90）kPa,95% CI（11.33,12.02）kPa。男性与女性间肝、脾弹性测量值差异均有统计学意义（P均<0.05）。年龄、BMI与肝、脾弹性模量值均无明显相关性。男、女性中,肝与脾弹性模量值均无相关性（P均>0.05）。结论 SWE可用以定量评价正常脾脏组织硬度。     

Analysis of sequential ultrasound frames for the measurement of hemodynamic stresses,critical bent buckling pressure,and critical buckling torque of human common carotid atherosclerosis

BackgroundStructural properties of the arterial wall are important diagnostic parameters. The current study aimed at investigating the hemodynamic properties and intima-media thickness changes of the common carotid artery in human subjects with atherosclerosis in order to determine the relationships between these indices.MethodsThis study presented methods to detect instantaneous changes in the lumen diameter, intima media thickness, longitudinal movement and acceleration, and velocity of the left side of common carotid artery. These parameters were measured in 155 male patients, categorized into control (n = 42), mild (n = 39), moderate (n = 37), and severe (n = 37) carotid stenosis groups by B-mode and Doppler ultrasonography. Extracted parameters were used to estimate the biomechanical properties of arteries, including radial strain, arterial stiffness index, Young's elastic modulus, circumferential stress, shear stress, axial stress, critical bent buckling pressure, and critical buckling torque.FindingsAll biomechanical parameters of common carotid artery were significantly different in patients with mild, moderate, and severe stenosis, compared to the control group (P < 0.05). Moreover, the current results showed a significant correlation between intima media thickness and non-intima media thickness-based biomechanical indices including circumferential strain, stiffness index, and shear stress in different stenosis groups (P < 0.05).InterpretationWe concluded that the conventional and new indicators such as axial stress, critical bent buckling pressure, critical buckling torque could be useful for evaluating atherosclerosis development and also, may provide more information for physicians and interventional radiologists in designing strategies for decreasing risk in interventional treatment such as stent replacement and differentiation of vulnerable plaques.     

Contradictory working length effects in locked plating of the distal and middle femoral fractures―a biomechanical study

BackgroundWorking length have been reported to affect the plate stress and fixation stiffness. However, the results of previous studies have been controversial. The present study was to determine working length effects on different locations of femoral bone gap.MethodsFive composite femurs with wide bone gaps at five levels (G1, 2, 3, 5, and 7), were fixed with locking plates. G1-3, G5 and G7 represented gaps at distal femur, distal-middle femur and middle femur respectively. Strain gauges were applied near the screw holes. The plate-bone constructs were loaded through a hemicylinder on the femoral head with total constraints at the distal femur. The micro-strains, axial stiffness and interfragmentary motions were recorded. Then the locking screws were removed one by one and the tests were re-run. The working length effects were compared and correlated.FindingsIn distal femurs (G1-3), long working length was negatively correlated with the highest strains (r = −0.97, −0.95 and − 0.95, p < 0.01) and axial stiffness (r = −1, −0.96 and −0.99, p < 0.01). In distal-middle femurs (G5), as the working length increased, the highest strain decreased initially and then increased (r = 0.81, p = 0.026) and the axial stiffness decreased (r = −0.98, p < 0.01). In middle femurs (G7), the highest strain and gap motions were much higher than that in the other groups and not significantly correlated with the working length change.InterpretationLong working length could reduce the highest plate strain in distal femurs, but had no significant effects in middle femurs. The working length effects were markedly affected by the loading and boundary conditions.     

Mechanical muscle and tendon properties of the plantar flexors are altered even in highly functional children with spastic cerebral palsy

BackgroundRecent ultrasound studies found increased passive muscle stiffness and no difference in tendon stiffness in highly impaired children and young adults with cerebral palsy. However, it is not known if muscle and tendon mechanical properties are already altered in highly functional children with cerebral palsy. Therefore, the purpose of this study was to compare the mechanical and material properties of the plantar flexors in highly functional children with cerebral palsy and typically developing children.MethodsBesides strength measurements, ultrasonography was used to assess gastrocnemius medialis and Achilles tendon elongation and stiffness, Achilles tendon stress, strain, and Young's modulus in twelve children with cerebral palsy (GMFCS levels I and II) and twelve typically developing peers during passive dorsiflexion rotations as well as maximum voluntary contractions.FindingsDespite no difference in ankle joint stiffness (P > 0.05) between groups, passive but not active Achilles tendon stiffness was significantly decreased (− 39%) and a tendency of increased passive muscle stiffness was observed even in highly functional children with cerebral palsy. However, material properties of the tendon were not altered. Maximum voluntary contraction showed reduced plantar flexor strength (− 48%) in the cerebral palsy group.InterpretationEven in children with mild spastic cerebral palsy, muscle and tendon mechanical properties are altered. However, it appears that the Achilles tendon stiffness is different only when low forces act on the tendon during passive movements. Although maximum voluntary force is already decreased, forces acting on the Achilles tendon during activity appear to be sufficient to maintain typical material properties.